I have encountered a few issues during the FCS installation. The FCS log file wasn't really helpful. Here are some of my observations during my FCS installation:
FCS Pre-requisite Failed: Unfortunately, the FCS log file (%Program Files%\Microsoft Forefront\Client Security\Server\Logs) is not that helpful. Go through MOM installation log file for detailed information. From my experience, most FCS pre-requisite issues are due MOM installation or pre-requite issues.
SQL Reporting Service: if the SQL reporting service is not running on port 80 (or default), your installation is going to fail. I know it is bad but the dashboard links in the FCS Management console are hard coded, so even if we can get past the install, those are going to fail if it's not running on the default port. So make sure SQL Reporting service is running on port 80
SQL Named Instance: You can use a name SQL instance without any issues.